The growth of algae is receiving a significant amount of attention due to its perceived uses as a source of combustible fuel, a source of nourishment, and as a raw material for biodegradable plastics, a consumer of carbon dioxide which is widely viewed as a threat to the environment. Most forms of algae require light to thrive. In light of the anticipated demand for algae, it would be preferable to grow algae in large tanks, for example tanks having a diameter of about 80 meters and a height of about 20 meters. If such tanks are intended to grow algae on a continuous basis, there is a need to supply light throughout the interior of the tank. Light simply directed on the top or outside surfaces of the tank, even if the tank was formed of a transparent material, would be inadequate since the algae close to the surface and sidewalls of the tank would block infiltration of light into the interior of the tank. Improved devices and illumination systems for providing illumination to submerged environments, e.g. bioreactors, are needed.